For mechanisms having one portion that rotates relative to another, it is often necessary to know the precise relative rotational position between the two portions. There are many types of sensor arrangements that can accomplish such a task; however, many have drawbacks in that they are too large for a particular application, too expensiv e to design and fabricate, or require extensive calibration once assembled in the mechanism.
These types of sensors can be used, for example as throttle position sensors, fuel accumulators, transmission position sensors, steering angle sensors, and gear tooth sensors. Many other types of applications of course can also benefit from having rotational position sensing.
Also, of course, it is desirable that the sensor be as inexpensive and easy to fabricate and assemble as possible in order to minimize the cost of the sensor assembly.
An additional requirement for some positional sensor applications is that there is a backup sensor or some other means of detecting a failure in part of the sensor assembly. In this way, if part of the sensor does fail, the appropriate actions can be taken to assure that no harm is done until the sensor can be fixed or replaced.
Consequently, it is desirable to have a rotational position sensor that does not need calibration, or may need only minimal calibration, is small in size, cost effective, and still reliable, with feedback if a failure of a portion of the sensor assembly occurs.